A mathematical pharmacokinetic and pharmacodynamic model was initially developed which can be used in the clinical operating room setting without interfering with routine clinical care. We determined the pharmacokinetics and pharmacodynamics of commonly used neuromuscular blocking drugs (d-tubocurarine and pancruonium) and common antagonists of a non-depolarizing neuromuscular blockade (neostigmine and pyridostigmine). In order to complete these studies a suitable assay to measure drug concentration in body fluids had to be developed. We implemented an immunoassay technique for measuring d-tubocurarine; a high performance liquid chromatography method was developed for measuring neostigmine and pyridostigmine in body fluids. Most recently, a mass spectrometry method was developed for measuring pancuronium concentrations in body fluids. We then determined the influence of renal failure, hepatic disease and hypothermia on the pharmacokinetics and pharmacodynamics of the drugs listed above.